How do i access the methods for the Virtual Reality addon?
Ok, I found out what the problem is.  I looked at the code for the virtual reality addon, and it wants a context argument for bpy.ops.view3d.virtual_reality_display.poll() Now unfortunately, I don't know what it wants for that argument, so you'll have to figure that out. 
Hope this helps!

UPDATE:
context MIGHT be bpy.context, but I can't test it so I'm not sure.